PCB Technical - Single-layer FPC/Double-sided FPC/Multi-layer FPC

Electronic products all use PCB, and the market trend of PCB is almost the vane of the electronics industry. With the development of high-end and miniaturized electronic products such as mobile phones, notebook computers and PDAs, the demand for flexible PCBs (FPCs) is increasing. PCB manufacturers are accelerating the development of thinner, lighter and denser FPCs. Let me introduce to you the types of FPC.

One, single-layer FPC

has a chemically etched conductive pattern, and the conductive pattern layer on the surface of the flexible insulating substrate is a rolled copper foil. The insulating substrate can be polyimide, polyethylene terephthalate, aramid cellulose ester and polyvinyl chloride. Single-layer FPC can be divided into the following four sub-categories:

1. Single side connection without covering layer

The wire pattern is on the insulating substrate, and there is no covering layer on the wire surface. The interconnection is realized by soldering, welding or pressure welding, which is commonly used in early telephones.

2. Single side connection with cover layer

Compared with the previous type, it only has an extra layer of coating on the surface of the wire. The pads need to be exposed when covering, and it can simply be left uncovered in the end area. It is the most widely used and widely used single-sided flexible PCB. It is used in automotive instruments and electronic instruments.

3. Double-sided connection without covering layer

PCB circuit board double-sided circuit board

The connection pad interface can be connected on the front and back of the wire. A via hole is opened on the insulating substrate at the pad. This via hole can be punched, etched or made by other mechanical methods at the required position of the insulating substrate. become.

4. There is a cover layer to connect on both sides

The front type is different, the surface has a covering layer, and the covering layer has via holes, allowing both sides to be terminated, while still maintaining the covering layer. It is made of two layers of insulating materials and a layer of metal conductors.

Two, double-sided FPC

Double-sided FPC has a conductive pattern made by etching on both sides of the insulating base film, which increases the wiring density per unit area. The metallized hole connects the patterns on both sides of the insulating material to form a conductive path to meet the design and use function of flexibility. The cover film can protect single and double-sided wires and indicate where the components are placed. According to requirements, metallized holes and cover layers are optional, and this type of FPC has fewer applications.

Circuit board PCB

Three, multi-layer FPC

Multi-layer FPC is to laminate 3 or more layers of single-sided or double-sided flexible circuits together, and form metallized holes by drilling and electroplating to form conductive paths between different layers. In this way, there is no need to use a complicated welding process. Multilayer circuits have huge functional differences in terms of higher reliability, better thermal conductivity and more convenient assembly performance.

The advantage is that the base film is light in weight and has excellent electrical properties, such as low dielectric constant. The multi-layer flexible PCB board made of polyimide film as the base material is about 1/3 lighter than the rigid epoxy glass cloth multi-layer PCB board, but it loses the excellent single-sided and double-sided flexible PCB. Most of these products do not require flexibility. Multi-layer FPC an be further divided into the following types:

1. Flexible insulating substrate finished product

This category is manufactured on a flexible insulating substrate, and the finished product is specified to be flexible. This structure usually bonds the two-sided ends of many single-sided or double-sided microstrip flexible PCBs together, but the central parts of them are not bonded together, thus having a high degree of flexibility. In order to have a high degree of flexibility, a thin, suitable coating, such as polyimide, can be used on the wire layer instead of a thicker laminated cover layer.

2. Finished soft insulating base material

This category is manufactured on a flexible insulating substrate, and the finished product is not specified to be flexible. This type of multilayer FPC is made of flexible insulating materials, such as polyimide film, laminated to make a multilayer board, which loses its inherent flexibility after lamination.